1. Field of the Invention
The present invention relates to a secondary battery and a method for manufacturing the same in embodiments thereof.
2. Description of the Related Art
Recently, a lithium secondary battery, which is rechargeable and lightweight and has a high energy and power density, has been widely used as an energy source for wireless mobile devices. Further, as a solution to the problems such as air pollution and the greenhouse house effect which are caused by existing internal combustion engine vehicles using fossil fuels such as a gasoline vehicle and a diesel vehicle, a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), a battery electric vehicle (BEV), an electric vehicle (EV), or the like have been proposed. The lithium secondary battery may serve as a power source for the alternative vehicles.
The lithium secondary battery is classified into a lithium ion battery using a liquid electrolyte and a lithium polymer battery using a polymer electrolyte in terms of a type of electrolytic solutions. The lithium secondary battery is also classified into cylindrical, prismatic, and a pouch shapes in terms of a shape of an exterior material in which an electrode assembly is housed.
Among these, the pouch type lithium secondary battery is made of a metal layer (foil) and a pouch film which is formed of multi-layered synthetic resin layers and coated on upper and lower surfaces of the metal layer, the weight of the pouch type lithium secondary battery may be remarkably lighter than that of the cylindrical lithium secondary battery or the prismatic lithium secondary battery using a metallic can. Thus, the pouch type lithium secondary battery may be lightweight and may be amenable to a change in shape.
FIG. 1 is a development view of a conventional pouch shape secondary battery 10 which is disclosed in Korean Patent Laid-Open Publication No. 10-2013-0089614 (2013 Aug. 12), and FIG. 2 is a cross-sectional view of the pouch shape secondary battery 10 of FIG. 1.
Referring to FIGS. 1 and 2, the pouch shape secondary battery 10 is formed by packaging an electrode assembly 1, to which an electrode tab 2 is attached, with an exterior material 3. The exterior material 3 includes a sealing portion 4 and a pair of pouch films 5. Each of the pair of pouch films 5 includes a forming portion 6 to house the electrode assembly 1. When a middle portion of the exterior material 3 is folded, upper and lower parts of the electrode assembly 1 are housed in the pair of forming portions 6.
The forming portion 6 is formed by pressing an inside of the pouch film 5 with a press or the like to allow the pouch film 5 to have a predetermined depth. In this regard, the depth at which the forming portion 6 may be formed about 7 mm at maximum, and therefore a thickness of the electrode assembly 1 housed in the forming portion 6 has also a depth limitation (about 14 mm). Therefore, a capacity of the secondary battery 10 has a limitation.